The present invention relates to an assembly including a wheel or an integral rim, for mounting a tire, and a tread support ring, which assembly is particularly useful in the case of a tire travelling at an abnormally low inflation pressure compared with the recommended pressure or even at zero inflation pressure. It also relates to the mounting rim as such, and to the tread-bearing support as such.
The main difficulties encountered in the case of travelling with a flat tire or at low pressure relate to the risk of unwedging of the beads of the tire, and in particular the unwedging of the bead of the tire located on the outside of the vehicle. The well-known proposed techniques for avoiding such unwedging, and in particular that consisting of arranging axially to the inside of the outer rim seat a protrusion or hump of low height, do not appear to give complete satisfaction and tend to increase the difficulties of mounting and dismounting the tires.
Patent EP 0 673 324, in order to overcome the above difficulties, describes a rolling assembly including a tire and an integral rim with two rim seats which are described as inclined towards the outside and extended axially towards the outside by two protrusions or humps of low height. The seat of the rim that will be located to the outside of the vehicle is extended axially towards the inside by a bearing surface intended and suitable to receive a tread-bearing support. The rim seat located to the inside of the vehicle is extended axially towards the inside by a rim flange, which flange is connected to the bearing surface by means of a mounting groove. The preferred variant of the rim comprises two seats inclined towards the outside and of unequal diameters, the seat located to the outside of the vehicle having a diameter less than the diameter of the seat located to the inside of the vehicle. The tread-bearing support of the assembly is made of elastically deformable, ovalisable elastomeric material that can be slipped on to the bearing surface. The tread-bearing support, as its name indicates, has the effect of preventing collapse of the tread in the event of inflation pressure loss, and thus permits the tire to travel at an acceptable deflection despite the lack or absence of inflation gas, while securely holding the outer bead of the tire in position on its rim seat.
Although it represents an enormous advance over the previously known systems for travel under conditions of low or zero inflation, which may be referred to as xe2x80x9ctravel in degraded modexe2x80x9d, and at the same time permits excellent performance during normal travel, the assembly described above has the disadvantage of being heavy.
For a consequent reduction in weight, it is possible to act effectively on the two elements of the assembly, namely the rim and the tread-bearing support. European applications EP 0 807 539 and EP 1098779 describe such lighter-weight rims which comprise either a bearing surface provided with a large number of recesses, or a bearing surface which amounts to two circumferential bearing zones separated axially by a circumferential groove. As for the tread-bearing support, it has been made significantly lighter by replacing a major part of the solid body, between the base and the apex of the support, with numerous recesses separated by solid partitions, of suitable form and position. European Application EP 1000774 and International Application WO 00/76791 describe such supports, which are also used for blocking at least the tire bead mounted on the rim seat located to the outside of the vehicle, which is of smaller diameter.
International Application WO 01/08905, in order to obtain a more lightweight assembly, proposes reducing the width of the tread-bearing support relative to the width of the support-bearing surface, and describes the means necessary for axially holding the tread-bearing support. Such means consists of providing the radially inner face of the support with at least one protuberance, which protuberance butts up against the wall(s) of (a) circumferential groove(s) formed in the bearing surface of the rim, which bearing surface is intended precisely to receive the tread-bearing support. Providing a metallic object with grooves, and more particularly a mounting rim for a tire, has several drawbacks: it is not always easy to form such grooves owing to the manufacturing process for the rim, and this is even more difficult when the groove(s) is (are) of small dimensions. Furthermore, any groove includes the presence of a groove bottom with connecting fillets, whether circular or not, and fillets of small dimension generally entail a concentration of stresses and the possibility of cracks appearing in the fillets.
In order to make an assembly of the type in question, i.e., formed of a rim comprising a tread-support bearing surface located between first and second rim seats and of a tread-bearing support, lighter, while overcoming the aforementioned drawbacks and thus permit better fatigue resistance of the mounting rim, the invention proposes providing the rim bearing surface, which is intended to receive the tread-bearing support, with a circumferential protuberance or rib which is housed in a groove in the radially inner face of the tread-bearing support.
The assembly according to the invention, therefore, includes an elastically deformable, circumferentially inextensible tread-bearing support, which can be slipped on to a suitable rim bearing surface extending a first rim seat axially towards the inside, and the minimum diameter of which is at least equal to the diameter of any rim part between the axially outer end of the bearing surface and the end of the protrusion or hump of low height, axially extending to the outside the first rim seat which is inclined towards the outside, a second rim seat having, viewed in meridian section, a generatrix, the axially inner end of which is located on a circle of diameter greater than the diameter of the circle on which is located the axially inner end of the first rim seat, the two seats being, axially to the inside, extended by frustoconical portions of a height at least equal to 0.01 times the minimum diameter of the bearing surface and the generatrices of which form with the axis of rotation angles xcex1 at least equal to 45xc2x0, wherein the rim bearing surface is provided with at least one circumferential protuberance of height h, arranged in a circumferential groove in the radially inner face of the tread-bearing support, such that the protuberance axially comes to bear against, and butt up against, at least one lateral wall of the groove.
As used herein, the term xe2x80x9cminimum diameterxe2x80x9d of the rim bearing surface, as measured in the plane parallel to the equatorial plane containing that circular end of the rim bearing surface that is closest to the first rim seat, is to be understood to mean the maximum distance between two diametrically opposed points of such circular end.
As used herein, the term xe2x80x9cprotrusion or hump of low heightxe2x80x9d, taking into account the dimensions of the rims in question and the dimensions of the tires required to be mounted on such rims, is to be understood to mean a protrusion or hump, the height of which is at most equal to 2.5% of the minimum diameter of the rim bearing surface.
The circumferential protuberance is preferably of low axial and radial dimensions, such dimensions being between 0.005 and 0.02 times the diameter of the rim bearing surface. The protuberance of the rim bearing surface then becomes lodged in the groove, substantially of the same dimensions, in the inner face of the tread-bearing support and butted up against the two lateral walls of the groove.
The circumferential groove of the tread-bearing support may, on the other hand, be of relatively large dimensions. A protuberance of the rim bearing surface may then come axially into contact with, and butt up against, a single one of the walls of the circumferential groove.
To avoid excessive difficulties in mounting the tread-bearing support on the rim bearing surface, it is in all cases advantageous for the axial distance between (1) the end, taken on the generatrix of the bearing surface, of the generatrix of the circumferential bearing groove closest to the second rim seat, and (2) the axial end of the tread-bearing support closest to the same second seat, to be at most equal to 0.3 times the axial width 1 of the radially inner face of the tread-bearing support.
To the same effect, the tread-bearing support is reinforced, in its radially inner part, by an armature of reinforcement elements which is divided into two parts: a first part axially on the side of the first rim seat, located at a radial distance from the base of the tread-bearing support which is at most equal to the height h of the protuberance, and a second part axially on the side of the second rim seat, which is located radially at a distance from the base of the support that is greater than the height h of the protuberance.
Still with the aim of facilitating mounting of the tread-bearing support on the rim bearing surface, the protuberance of the bearing surface preferably has a meridian section, the lateral face of which closest to the first rim seat is of frustoconical shape and has a generatrix which forms with the axis of rotation of the assembly an angle xcex2 which may be between 15 and 45xc2x0. The lateral face of the protuberance closest to the second rim seat is also of frustoconical shape, and has a frustoconical generatrix which forms with the axis of rotation an angle "khgr" of between 70 and 90xc2x0, the two generatrices possibly being joined by a circular arc or a straight-line segment. It is understood that the boundaries may be taken by the angles xcex2 and "khgr".
Preferably, the maximum diameter of the protuberance of the bearing surface is at most equal to the diameter of the axially outer end of the second rim seat, with the aim of not creating difficulties in mounting the tire, which is intended to complete the assembly.